The lymphocyte antigen CD27 is a cytokine receptor found on the surface of most human T lymphocytes and some B lymphocytes. A cDNA encoding the CD27 receptor has been isolated (Camerini et al., J. Immunol. 147:3165, (1991). Based on the predicted polypetide sequence, CD27 belongs to a family of cysteine-rich receptors whose known ligands include nerve growth factor, and TNF-.alpha. and -.beta.. Structural similarities suggest that CD27 belongs to a lymphocyte-specific subgroup of the family comprised of the B cell Ag CD40, the rat T cell subset Ag OX40, and the mouse T cell activation Ag 4-1BB. The CD27 receptor is believed to mediate functions which allow survival of activated cells.
The growth factor responsible for binding to and initiating CD27 activities has not yet been identified. The existence and nature of such growth factors will be important in elucidating mechanisms for survival of activated cells. A need has thus existed for identifying and characterizing a ligand that binds to CD27.